The maze operation is a newly developed surgical procedure for patients with chronic atrial fibrillation. Between may 1993 and october 1994, 11 patients underwent mitral valve surgery combined with the maze procedure, 10 for chronic, medically refractory, symptomatic atrial fibrillation and 1 for intermittent, symptomatic atrial flutter. In one patient, a double aorto-coronary venous bypass was added. The operative mortality was 9%: one patient died on the 7th postoperative day from a perioperative cerebrovascular accident. Postoperatively, electrophysiological and stress testing as well as transthoracic or transesophageal echocardiography (TTE; TEE) were performed. All patients were in sinus rhythm. Left and right atrial contractions were analyzed by TTE/TEE and the atrial transport function was documented in each patient. The postoperative exercise stress test revealed slight sinus-node incompetence. After a mean follow-up time of 10.4 +/- 5.4 months (1 to 16 months) all surviving patients are free from atrial fibrillation or flutter and without need for medication. The maze operation, which we performed for the first time in connection with mitral valve surgery, is a successful treatment for chronic, medically refractory atrial fibrillation and intermittent, symptomatic atrial flutter. This procedure provides a sinus rhythm with atrioventricular synchrony, restores the atrial transport function and obviates the need for antiarrhythmic drugs. Long-term anticoagulation appears unnecessary.